Filtering Data with Invalid Field Values Based on Another Table

In this article, we will explore how to filter data in one table based on the validity of field values from another table. We’ll use SQL Server as our database management system, but the concepts and syntax can be applied to other RDBMS variants.

Problem Statement

Given two tables, FirstTable and Movies, with a common column Name, we want to filter data in the Movies table that has invalid gender values based on the corresponding records in the FirstTable. We’ll assume that valid male and female genders are represented by integers 1 and 2, respectively.

Solution Overview

To solve this problem, we can use a combination of JOIN, LEFT JOIN, and filtering techniques. Our approach will involve:

1. Filtering out records from the Movies table where there is no matching record in the FirstTable.
2. Using a LEFT JOIN to join the filtered data with the corresponding records in the FirstTable.
3. Applying filtering conditions to remove rows that have valid gender values.

Step 1: Filter Out Records with No Matching Name

To ensure we only consider records from the Movies table where there is a matching record in the FirstTable, we can use an additional filter condition:

SELECT Id, 
       tmp.Name, 
       ActorName,      
       ActorGender,
       ReleaseDate
FROM Movies tmp 
JOIN FirstTable gn on tmp.ActorName = gn.Name

This will only consider rows where there is at least one matching record in the FirstTable.

Step 2: Use LEFT JOIN to Match Gender Values

Next, we’ll use a LEFT JOIN to match the gender values between the Movies table and the corresponding records in the FirstTable. This will ensure that all filtered rows are included in the results, even if there is no matching record in the FirstTable.

SELECT Id, 
       tmp.Name, 
       ActorName,      
       ActorGender,
       ReleaseDate
FROM Movies tmp 
LEFT JOIN FirstTable gn on tmp.ActorName = gn.Name AND tmp.ActorGender = gn.Gender

Step 3: Apply Filtering Conditions

Finally, we’ll apply filtering conditions to remove rows that have valid gender values. In this case, we want to include only rows where the gender value in the Movies table does not match the corresponding record in the FirstTable.

SELECT Id, 
       tmp.Name, 
       ActorName,      
       ActorGender,
       ReleaseDate
FROM Movies tmp 
LEFT JOIN FirstTable gn on tmp.ActorName = gn.Name AND tmp.ActorGender = gn.Gender
WHERE gn2.Name IS NULL OR gn2.Name != gn.Name

This condition will filter out rows where the gender value in the Movies table matches a valid record in the FirstTable, and also exclude rows where there is no matching record.

Step 4: Final Results

The final results should include only rows from the Movies table that have invalid gender values based on the corresponding records in the FirstTable.

Id  Name        ActorName   ActorGender     ReleaseDate
2   Movie 2     Kevin       2               22/12/2018 07:20:14
5   Movie 5     Clare       1               22/12/2018 07:20:14
8   Movie 8     Sara        1               22/12/2018 07:20:14
13  Movie 13    Kevin       2               22/12/2018 07:20:14

Conclusion

In this article, we demonstrated how to filter data in one table based on the validity of field values from another table using SQL Server and JOIN, LEFT JOIN, and filtering techniques. By applying these steps, you can identify rows that have invalid gender values and exclude them from your results.

Remember to always consider edge cases and test your queries thoroughly to ensure accurate results. Happy querying!

Last modified on 2023-10-03